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share/man/man4/tcp.4
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | ||||
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | ||||
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | ||||
.\" SUCH DAMAGE. | .\" SUCH DAMAGE. | ||||
.\" | .\" | ||||
.\" From: @(#)tcp.4 8.1 (Berkeley) 6/5/93 | .\" From: @(#)tcp.4 8.1 (Berkeley) 6/5/93 | ||||
.\" $FreeBSD$ | .\" $FreeBSD$ | ||||
.\" | .\" | ||||
.Dd April 8, 2021 | .Dd April 17, 2021 | ||||
.Dt TCP 4 | .Dt TCP 4 | ||||
.Os | .Os | ||||
.Sh NAME | .Sh NAME | ||||
.Nm tcp | .Nm tcp | ||||
.Nd Internet Transmission Control Protocol | .Nd Internet Transmission Control Protocol | ||||
.Sh SYNOPSIS | .Sh SYNOPSIS | ||||
.In sys/types.h | .In sys/types.h | ||||
.In sys/socket.h | .In sys/socket.h | ||||
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(default is true). | (default is true). | ||||
.It Va do_prr_conservative | .It Va do_prr_conservative | ||||
While doing Proportional Rate Reduction, remain strictly in a packet conserving | While doing Proportional Rate Reduction, remain strictly in a packet conserving | ||||
mode, sending only one new packet for each ACK received. | mode, sending only one new packet for each ACK received. | ||||
Helpful when a misconfigured token bucket traffic policer causes persistent | Helpful when a misconfigured token bucket traffic policer causes persistent | ||||
high losses leading to RTO, but reduces PRR effectiveness in more common settings | high losses leading to RTO, but reduces PRR effectiveness in more common settings | ||||
(default is false). | (default is false). | ||||
.It Va rfc6675_pipe | .It Va rfc6675_pipe | ||||
Calculate the bytes in flight using the algorithm described in RFC 6675, and | Deprecated and superseded by | ||||
is also an improvement when Proportional Rate Reduction is enabled. | .Va sack.revised | ||||
Also enables two other mechanisms from RFC6675. | |||||
Rescue Retransmission helps timely loss recovery, when the trailing segments | |||||
of a transmission are lost, while no additional data is ready to be sent. | |||||
In case a partial ACK without a SACK block is received during SACK loss | |||||
recovery, the trailing segment is immediately resent, rather than waiting | |||||
for a Retransmission timeout. | |||||
SACK loss recovery is also engaged, once two segments plus one byte are | |||||
SACKed - even if no traditional duplicate ACKs were seen. | |||||
.It Va rfc3042 | .It Va rfc3042 | ||||
Enable the Limited Transmit algorithm as described in RFC 3042. | Enable the Limited Transmit algorithm as described in RFC 3042. | ||||
It helps avoid timeouts on lossy links and also when the congestion window | It helps avoid timeouts on lossy links and also when the congestion window | ||||
is small, as happens on short transfers. | is small, as happens on short transfers. | ||||
.It Va rfc3390 | .It Va rfc3390 | ||||
Enable support for RFC 3390, which allows for a variable-sized | Enable support for RFC 3390, which allows for a variable-sized | ||||
starting congestion window on new connections, depending on the | starting congestion window on new connections, depending on the | ||||
maximum segment size. | maximum segment size. | ||||
This helps throughput in general, but | This helps throughput in general, but | ||||
particularly affects short transfers and high-bandwidth large | particularly affects short transfers and high-bandwidth large | ||||
propagation-delay connections. | propagation-delay connections. | ||||
.It Va sack.enable | .It Va sack.enable | ||||
Enable support for RFC 2018, TCP Selective Acknowledgment option, | Enable support for RFC 2018, TCP Selective Acknowledgment option, | ||||
which allows the receiver to inform the sender about all successfully | which allows the receiver to inform the sender about all successfully | ||||
arrived segments, allowing the sender to retransmit the missing segments | arrived segments, allowing the sender to retransmit the missing segments | ||||
only. | only. | ||||
.It Va sack.revised | |||||
Enables three updated mechanisms from RFC6675 (default is true). | |||||
Calculate the bytes in flight using the algorithm described in RFC 6675, and | |||||
is also an improvement when Proportional Rate Reduction is enabled. | |||||
Next, Rescue Retransmission helps timely loss recovery, when the trailing segments | |||||
of a transmission are lost, while no additional data is ready to be sent. | |||||
In case a partial ACK without a SACK block is received during SACK loss | |||||
recovery, the trailing segment is immediately resent, rather than waiting | |||||
for a Retransmission timeout. | |||||
Finally, SACK loss recovery is also engaged, once two segments plus one byte are | |||||
SACKed - even if no traditional duplicate ACKs were observed. | |||||
.It Va sack.maxholes | .It Va sack.maxholes | ||||
Maximum number of SACK holes per connection. | Maximum number of SACK holes per connection. | ||||
Defaults to 128. | Defaults to 128. | ||||
.It Va sack.globalmaxholes | .It Va sack.globalmaxholes | ||||
Maximum number of SACK holes per system, across all connections. | Maximum number of SACK holes per system, across all connections. | ||||
Defaults to 65536. | Defaults to 65536. | ||||
.It Va maxtcptw | .It Va maxtcptw | ||||
When a TCP connection enters the | When a TCP connection enters the | ||||
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